1. Field of the Invention
The present invention relates to a forming method of a diamond film and a device for forming the diamond film, and more particularly to a method and a device for forming a diamond film under a comparatively low pressure by making use of an arc discharge.
2. Description of the Prior Art
Conventionally, diamond has been formed by processing carbon powder such as graphite powder in the presence of metallic catalyst at a high temperature and under a ultra-high pressure.
Recently, methods for forming diamond under a low pressure have been noted in place of the above described conventional method. And such methods by which diamond is practically formed, can be roughly classified into following three types of method.
A first type of method is called a heat filament chemical vapour deposition (CVD) method. According to this method, a tungsten filament is disposed just above a substrate which is heated at 800.degree. through 1000.degree. C., this filament is heated at 2000.degree. C. or more, and a mixture gas of hydrogen and hydrocarbon such as methane is sprayed to the substrate through the heated filament thereby to grow a diamond film on the substrate.
A second type of method is called a microwave plasma CVD method. According to this method, a plasma is generated in a mixture gas of hydrogen and hydrocarbon by the function of microwave of hundreds wat to grow a diamond film on a substrate which is positioned within the generated plasma. At this time. the substrate is heated by the microwave to about 700.degree. though 900.degree. C. High frequency wave plasma generated by high frequency wave of 13.56 MHz can be substituted for the above described microwave plasma.
In the above described two types of methods, atomic hydrogen accelerates the decomposition of methane and prevents the formation of other synthetic material such as amorphous carbon selectively.
A third type of method is a method using ion beam. According to this method, a diamond film is growed on the substrate by irradiating the substrate with ion beam of carbon. In this case, an arc discharge can be used for generating the ion beam (Japanese unexamined patent publication Sho 58-91100).
The above described conventional forming methods of the diamond film have following problems. Namely, in the heat filament CVD method, the heated filament is broken at not less than 2000.degree. C. which is the melting point of tungsten. Accordingly, sufficient decomposition of the mixture gas cannot be realized so as to be not practical.
In the microwave plasma CVD method, the size of a plasma chamber is restricted and accordingly, it is difficult to apply this method to samples of a large area. Furthermore sufficient decomposition of the mixture gas, particularly hydrogen gas cannot be obtained.
By the forming method by ion beam, it has not been reported that diamond of high purity is formed. Only diamond containing a large amount of impurity such as amorphous carbon is formed.